Service providers may offer Ethernet-based connectivity to customers using the methods specified by Institute of Electrical and Electronics Engineers (IEEE) standard 802.1Q Virtual Local Area Network (VLAN) Bridging and its amendments, including IEEE 802.1ad Provider Bridging (PB) and IEEE 802.1ah Provider Backbone Bridging (PBB). IEEE 802.1Q specifies that the active components of a VLAN Bridged network must conform to a tree topology in order to avoid looping of frames. Such a tree topology may be maintained dynamically by a Spanning Tree Protocol (STP) or statically by provisioning or by the use of a network having a physical tree topology. A node that has only a single point of attachment to the tree (i.e., which lies at the edge of the tree) is called a leaf node. Any other node is called an interior node.
In the tree topology, data communications can be protected against link failures using the IEEE 802.3ad standard, also referred to as Link Aggregation. According to Link Aggregation, the data transported between two nodes is distributed among a plurality of links between those nodes, which are said to belong to a Link Aggregation Group (LAG). When a link fails, the data load assigned to that link can be reassigned or shifted to other available links in the LAG. Thus, Link Aggregation provides load distribution and protection against link failures without addressing node failures. Other methods have been proposed to support load distribution and to provide protection against both link and node failures. However, such methods may require establishing a virtual switch architecture, where the interior nodes are paired and interconnected via dedicated links or trunks to form a virtual interior node and hence provide redundancy against node or link failures. Accordingly, the interior node's functionality is modified or upgraded, which may not be desired by a service provider.